Physical and functional association of the cbl protooncogene product with an Src-family protein tyrosine kinase, p53/56lym, in the B cell antigen receptor-mediated signaling

Abstract

To identify novel signal transducers involved in signaling mediated by the Src-family protein tyrosine kinases (PTKs), we used a yeast two-hybrid system with a probe corresponding to the regulatory region of p56lym, a member of Src-family PTKs. One of the isolated clones contained the COOH-terminal 470 amino acid residues of p120c-cbl, the product of the cellular homologue of the v-cbl retroviral oncogene. p 120c-cbl is a cytoplasmic protein with nuclear proteinlike motifs. Here we show in vivo association of p120c-cbl with p53/56lym. After stimulation of the B cell antigen receptor (BCR), p120c-cbl was rapidly tyrosine phosphorylated. Studies with lyn- or syk-negative chicken B cells demonstrated that p53/56lym, but not p72syk, was crucial for tyrosine phosphorylation of p120c-cbl upon stimulation of the BCR. We also show the importance of p59fyn in tyrosine phosphorylation of p 120c-cbl in the T-cell receptor-mediated signaling, using fyn-overexpressing T cell hybridomas and splenic T cells from fyn-deficient mice. These results suggest that pl20c-cbl is an important substrate of Src-family PTKs in the intracellular signaling mediated by the antigen receptors.